1. Field of the Invention
This invention concerns an electric driving device and, specifically, it relates to an electric driving device for a camera in which various actuation members for photographing operations are driven by a motor.
2. Discussion of the Background
Focusing a lens on an object can be conducted by manual operation of a range ring of the lens in still cameras, cinecameras, TV cameras and the likes. By the way, the number of cameras having automatic focusing mechanisms is increasing in recent years. It is necessary for the focusing mechanism of this kind that the range ring of the lens is driven by a motor based on the information obtained from the means for detection of the state of the focusing.
A pulse motor having features capable of accurately and simply controlling the rotational angle has generally been used as a motor for driving the lens. On the other hand, the pulse motor also has a feature that the starting torque is smaller compared with other DC motors. In such a pulse motor, a battery is used as a power source by way of a constant voltage circuit or constant current circuit for reliably conducting the rotation, and particularly, starting. Further, the value of output voltage and output current is set to have such a sufficient margin that a reliable rotating operation can be conducted irrespective of voltage drop of the battery or fluctuations of the load torque.
Further, the pulse width of generated pulse signals is set constant with a sufficient margin based on various conditions.
The first problem in such a conventional lens driving device is that since the period of current supply to the pulse motor is set to have a sufficient margin for securing the starting torque, that is, it is set so as to drive the motor at a low speed, a considerable time is required for driving the lens to a predetermined position, as well as there is a loss of a current after the starting and it lowers the utilization efficiency of valuable battery power source. On the other hand, there is another problem that if the pulse width of the driving pulse is narrowed to obtain a high speed driving from beginning, the accuracy in the stopping position will be lowered and the starting torque will be insufficient as described above.
Further, in a conventional electric driving device for a camera, there is a case in which a plurality of actuation members conducting directly or indirectly the photographing operation is driven by one motor, for example, a motor for use on film winding. In this case, a shutter charging (so-called shutter setting) and a charging for driving the focus ring of a lens having an automatic focusing function, for example, from the focused position in the last photographing operation to the nearest or infinite (.infin.) side are conducted simultaneously or sequentially with the rotation of a motor during winding up a film.
And in this case, for popping up a strobo device previously stored by manual operation into a stored position (stowed position) by a half-depression stroke of a shutter release button, it is necessary to supply a magnet with a current based on light information measured by an automatic exposure control circuit (hereinafter simply referred to as : AE control circuit).
Then, current is supplied to a magnet for maintaining the charge of the shutter charged at last film winding to maintain the shutter at a stand-by state.
Then, current is supplied to a magnet for releasing lock of a focus ring charged at the last film winding and current is supplied to a locking magnet for locking the focus ring when a predetermined focusing is obtained.
When the shutter release button is further depressed deeper, current is supplied to a shutter-opening magnet to open the shutter. Then, current is supplied to a magnet for shutter-closing operation based on the light information measured by the AE control circuit to complete the film exposure, thereby completing a series of photographing sequence.
However, as the second problem of a conventional electric driving device for a camera, since a plurality of actuation members are charged by the driving force of a film winding motor and they are locked at the charged state by magnets, it requires a magnet for locking the shutter charge, a magnet for locking the focus ring, a magnet for releasing the locking of strobo locked at a stowed position and displacing it to the operating position etc., and accordingly, the cost is increased, the electrical power consumption is also increased and the battery life is reduced, particularly, in those cameras where the battery voltage is restricted at about several volts and a small capacity.
Furthermore, it also requires a circuit for conducting the control of the current supply to the magnets and results in a problem in those cameras for which reduction in the size is highly required.
Further, since it requires a mechanical governor for slowly displacing the lens and a mechanical governor for controlling the shutter time, as well as switches for detecting the lens position, the cost is increased.
Further, since it requires setting mechanisms for the respective actuation members as described above, it brings about an additional problem that the structure becomes complicated also in this respect.
Furthermore, there is another case in the conventional electric driving device for ordinary cameras in which a lens driving mechanism for moving a lens to a focused position and a mechanism for a shutter opening and closing according to predetermined time based on the measured intensity of light, are incorporated as separate mechanisms and they are actuated individually. It has been tried to conduct the lens driving and shutter opening and closing operation by a common motor instead of such conventional cameras.
However, the mechanism for the lens driving and shutter opening and closing by a common motor tried so far uses a magnet for stopping the lens at a focused position as described above. Accordingly, it requires a magnet and a driving circuit therefor in addition to the motor, which leads to a third problem.
Further, in the conventional cameras, a lens driving mechanism for moving the lens to focused position and a shutter mechanism for opening and closing the shutter for a predetermined time in accordance with the measured intensity of light, are incorporated as separate mechanisms and they are operated individually. In place of such a conventional camera, it has been attempted to conduct the lens driving and shutter opening and closing operations by a pulse motor.
In a mechanism for lens driving and shutter opening and closing by a pulse motor considered so far, the pulse motor is driven at a constant pulse rate and the rotational force of the pulse motor is used for lens driving and shutter opening and closing operations by way of a speed reduction mechanism. However, since the load at starting lens is greater than the load at shutter opening and closing operation, there is the fourth problem, that is, the torque of the pulse motor and the speed reduction ratio of the speed reduction mechanism have to be adjusted for lens driving operation requiring large load and, as a result, the size of the pulse motor is enlarged and the speed is lowered as a whole due to the increase in the speed reduction ratio.